Vapor-plating metals from fluorocarbon keto metal compounds



Dec. 5, 1967 w, osHuzR ET L 3,356,527

VAPOR-PLATING METALS FROM FLUOROCARBON KETO METAL COMPOUNDS Filed April25, 1964 Fri-04240 3 5 United States Patent Filed Apr. 23, 1964, Ser.No. 362,212

3 Claims. (Cl. 117107.2)

ABSTRACT OF THE DISCLOSURE Process for depositing a metal or an alloycoating on a hot target substrate by the reduction of a metal chelateselected from the group of copper, nickel, cobalt and leadacetonylacetonate, hydrates, halides, alkyl, aryl, hydroxyl andnitro-compounds at 250-500 C. and at one atmosphere of pressure.

The invention described herein may be manufactured and used by or forthe United States Government for governmental purposes without paymentto any of us of any royalty thereon.

This invention relates to the deposition of metals on substrates andmore particularly to the deposition on heated targets of metal coatingsby the reduction or the decomposition of halocarbon beta-diketonatemetal chelates, such illustratively as chelates of the metals copper,nickel, cobalt, lead and the like.

A metal chelate of a beta-diketone of the formulaR"R"R'C(:O)C'HRC(:O)CR"R"R wherein R is halogen and R", R, R"", and R isselected from the class consisting of hydrogen, halogen, alkyl,haloalkyl, perhaloalkyl, aryl, haloaryl, hydroxyl and nitro groups.Those members of the metal chelates of the formula cited above, whichare volatile at the temperatures disclosed herein, come within the scopeof the present invention.

The chelates in some instances may occur as solvates, as for examplecobalt (II) hexafluoroacetylacetonate hydrate or copper (II)hexafluoroacetylacetonate hydrate.

It has been common practice heretofore to deposit metal coatings fromthe metal vapor phase by decomposing the halides, carbides, hydrides orthe like, salts of the metals. The prior practices in general requirehigh temperatures in the order of from 600 C. to 1500 C., which severelylimits the substrates that can be plated.

The present invention, by comparison, discloses the plating of therepresentative metals copper, nickel, cobalt, lead and the like, fromtheir 1,l,1-trifiuoro-2,4-pentanedionato and1,1,l,5,5,S-hexafiuoro-Z,4-pentanedionato che lates at temperaturesabout in the range of from 250 to 500 C. and about at atmosphericpressure. These low temperatures permit the plating of these metals on abroadened range of materials, such as rubber, plastic, paper etc. thatwill survive these modest temperatures, as well as high temperatureceramics, metals and the like.

The object of the present invention is :the provision of means andmethods for depositing metal coatings from the gaseous phases atrelatively low working temperatures and about at atmospheric pressure.

Another object of this invention is to provide tightly adherentdeposited coatings of high purity metals by reactions that yield theelemental metal as the only nonvolatile component of the process.

A further object is to provide a plating system with easy control overthe rate of plating and the thickness of the metal plate deposit.

A further object is the provision of control over the mix- 3,356,527Patented Dec. 5, 1967 "ice tures of metals that form the plate, by adesired mixing of the vapors of a plurality of chelates used in theplating reaction to provide a desired allow of the metals involved.

Another object is to provide a means and a method for depositing metalsselectively on desired portions of the object to be plated, oncomplicated, intricate and embedded patterns, printed electricalcircuitry, and the like.

A generalized diagrammatical flow diagram of the metal plating apparatusused in practicing the present invention is illustrated in the singlefigure of the accompanying drawing.

In the drawing, hydrogen gas 1 at atmospheric pressure is passed intothe subliming chamber 2, Where a heat source 3 causes the chosen metalchelate 4 to sublime. The hydrogen gas serves functionally as both acarrier gas and as a reducing agent. The flow of the hydrogen gas causesthe vaporized chelate to pass from the subliming chamber 2 into theplating chamber 5.

Within the plating chamber 5 a second heat source 6 supplies heat to atarget assembly 7 at a controlled temperature for plating to occur onthe hot exposed surfaces of the target. The physical conditions at thesurface of the target 7 and the time of target exposure are controlledto provide the optimum desired plating results at a desired metalthickness.

The reaction products, such as hydrogen gas, unreacted chelate etc. arecarried by the hydrogen carrier gas from the plating chamber 5 into acold trap 8 where unreacted chelate, less volatile reaction products andthe like, are collected and from which the more volatile components aretreated further or are vented at 10 to the atmosphere. The unreactedhydrogen and regenerated chelating agent may be recycled advantageously.The cold trap 8 is immersed in a cold bath 9. The cold bath 9illustratively may contain a Dry Ice-acetone coolant or another desiredcoolant.

The heating units 3, 6, etc. for the subliming chamber 2 and the platingchamber 5, respectively, are advantageously selected from availabletypes that operate by induction, radiation, resistance etc.

The target 7 is of a chosen material that remains stable at the maximumtemperature to which it is subjected, and that is of a design thatallows a sufficient concentration of the chelate in the gaseous phase inthe proximity of the target surface to allow a satisfactory rate ofmetal deposition.

An illustrative cold trap 8 may be a single collector of one or morenon-volatile components in the vapors entering the cold trap, or it maybe comprised of a desired plurality of fraction collecting compartmentsat graduated temperatures for collecting separately and selectively, the

' unreacted chelate in a first zone, the regenerated chelating agent ina second zone of a lower temperature, etc.

Suitable precautions are taken to maintain the inner walls of theplating chamber at a temperature that is above the recrystallizationtemperature of the metal chelate to avoid the deposition of thevaporized chelate on the surfaces and yet not at temperatures highenough to cause deposition of the metal at undesired places on the Wallsof the chamber. The chamber inner Wall surfaces contacted by the vaporis preferably maintained slightly above the sublimation temperature ofthe particular chelate that is being caused to flow through theapparatus. The deposition heating element 6 is positioned to avoid thedeposition of metal thereon. In one form of the invention, the heatingelement 6 was positioned within the target 7. In another form of theinvention the heating element was wound outside of a cylindricaldeposition carbon monoxide or the like.

3 Example I In the application of a surface coat of copper on glass,such as on the surface of a glass tubing, or the like, a 0.1 gram sampleof copper hexafluoroacetylacetonate is weighed and placed in one end ofa glass tube that has a 1 centimeter inner diameter and that is 15inches in length. The glass tube that was plated experimentally was aborosilicate glass and its end that contained the sample was positionedas the metal chelate 4 in the subliming chamber 2 of the drawing and theremainder of the tube comprised the plating chamber in the drawing.

The carrier and reducing gas hydrogen is flowed through the glass tubeat an average velocity of about /2 inch per second.

During the deposition reaction, the portion of the tube containing thesample 4 is heated by the winding 3 at about 80 to 95 C. while theremainder of the tube, representing the plating chamber 5 is maintainedat a temperature of about 300 C. Copper is deposited in this latter,hotter zone on the inner surface of the glass tube at a rate ofthickness growth of about 800 A. per minute, in a band that is about 2inches in width. At the termination of the deposition run the copperplate was about 25,000 A. thick. The thickness of the plate may beincreased by the use of a higher concentration of the metal chelate inthe gas phase or by the use of longer plating times. The copper plate sodeposited on glass is of a high degree of purity, is electrically highlyconductive, shiny, ductile and adheres well to the glass. The excesschelate and less volatile reaction products including the regeneratedchelating agent, from the reaction is trapped in the cold trap 8 byimmersion in the Dry Ice-acetone bath 9. The excess hydrogen and morevolatile reaction products escape from the vent to the atmosphere.

Example 2 Cobalt is plated on a chosen metal, such as a ribbon ofstainless steel, laced as the target 7 in the plating chamber 5. A smallsample of cobalt II hexafiuoroacetylacetonate dihydrate, is placed at 4in the subliming chamber 2. The subliming chamber 2 is maintained atabout between 110 and 130 C. by means of the heat source 3. Hydrogen gasis caused to flow through the apparatus at the rate of about /2 inch persecond.

The vapor mixture so produced is passed from the subliming chamber 2into the plating chamber 5, Where the ribbon of stainless steel 7 ismaintained at about 350 C. by means of the heat source 6. The residualvapor is then, as before, passed through the cold trap 8 to theatmosphere.

Coatings of metals plated on supports in the making of printedelectrical circuits and the like, are readily accomplished by thetechniques disclosed herein.

The disclosed metals copper, nickel, cobalt, and lead are in the lowerpart of the electromotive series. Metals that appear to have platingpotentialities similar to those of copper, nickel, cobalt, and leadappear to be those below thallium in the series and include, molybdenum,tin, mercury, silver, rhodium, palladium, platinum and gold.

The technique that is disclosed herein has the further utility ofminimizing the erosion of a metal surface or replacing worn metalsurfaces, such for example as within a nozzle. The maximum wear on anozzle expelling hot gas occurs at the point of highest temperature andgreatest gas flow rate. The injection in the gas stream of a chelate ofthe nozzle lining metal and its decomposition yields the free metaldeposited as a coating that slows, stops, or that reverses the erosionof the nozzle lining metal.

The metal plating potentialities of the present invention include cobaltmemory cores for computers, metallized decorative plastics, metalplating on any surface that will withstand the modest depositiontemperature requirements disclosed herein, including the application ofabrasion resistance surfaces and linings on paper, rubber, plastics andthe like. Metal films of micro-thinness are of use in radiationdetection and counting, particle bombardment studies etc. in theproduction of films of precisely controlled thickness, purity andcompositions.

It is to be understood that the compounds, reactants, reagents,temperatures, pressures and reactions that are disclosed herein aresubmitted as operatively successful reductions to practice of at least athird of the group of metals that are contemplated hereby, and thatmodifications may be made in the present invention without departingfrom the spirit and the scope thereof.

The cobalt plate so deposited on the surface of the stainless steelribbon has a high degree of purity, has a high electrical conductivity,is shiny, ductile and adheres well to the metal substrate.

Example 3 Odd and intricate shapes are successfully plated in desiredpatterns by following the present process. Illustratively a glass tubewas plated with a spiral strip of copper plate on its inner surface byWinding a resistance wire spirally on the outside of the glass tube andmaintaining the spiral winding at 350 C. as the vaporized copper chelateof Example 1 is passed through the tube. The copper plate is depositedon the glass along the resistance wire spiral, using copperhexafluoroacetylacetonate at 4 as the metal chelate. The copper platemay be applied in lines, points or other desired patterns, and appearsas a brilliant, closely adherent film.

The temperatures at which experimental chelates sublime and at which thetargets are maintained are shown in the chart:

Both copper hexafiuoroacetylacetonate and coppertrifluoroacetylacetonate in a nitrogen or other inert gas atmosphere,deposits the copper on a target maintained at 350 to 500 C. It is notedtherefore that for some chelates such illustratively as coppertrifluoroacetylacetonate and copper hexafluoroacetylacetonate,deposition of the metal can be made to occur at the heated surfacewithout the presence of a reducing gas, such as the hydrogen cited here.

We claim:

1. The process of applying a metal coating to the surface of a substratetarget by heating a metal chelate selected from the group that consistsof fluorocarbon keto metal compounds that consists of thehexafluoroacetylacetonates and the trifluoracetylacetonates of themetals copper, nickel, cobalt II and lead to its sublimationtemperature, passing a reducing agent in vapor form over the metalchelate as a carrier gas, and decomposing the metal chelate in its vaporstate and depositing at least a part of the metal content of the chelateon the surface of a substrate target maintained at the depositiontemperature of the metal content of the chelate.

2. The process of applying a copper coating on the surface of asubstrate by passing a vapor selected from the group that consists ofcopper hexafluoroacetylacetonate and copper trifluoroacetylacetonatetogether with a reducing agent thereof over the substrate at 250500 C.temperature and at about one atmosphere of pressure in decomposing thevapor and applying a metal coating on the substrate.

3. The process of simultaneously depositing a plurality of metals as amixed metal coating forming a layer on a substrate by heating to theirvapor states a desired plurality of metal chelates selected from thehexafluoroacetylacetonates and the trifluoroacetylacetonates of thegroup of metals that consists of copper, nickel, cobalt H and lead,heating the substrate to the metal deposition temperature, combining thevaporous metal chelates with a reducing carrier gas, and conducting thecombined vaporous metal chelates and reduced carrier gas to the heatedsubstrate for causing the deposition on the substrate of a mixed metalcoating.

References Cited UNITED STATES PATENTS 2,430,520 11/1947 Marboe117-107.2 X 2,833,676 6/1958 Herbel et al 117107.2 X 2,898,227 8/1959Drummond 117107.2 X 3,092,511 6/1963 Edelman 117-1072 OTHER REFERENCESMartell et al., Chemistry of the Metal Chelate Compounds, 1957, page 180relied on.

ALFRED L. LEAVITT, Primary Examiner.

A. GOLIAN, Assistant Examiner.

1. THE PROCESS OF APPLYING A METAL COATING TO THE SURFACE OF A SUBSTRATETARGET BY HEATING A METAL CHELATE SELECTED FROM THE GROUP THAT CONSISTSOF FLUOROCARBON KETO METAL COMPOUNDS THAT CONSISTS OF THEHEXAFLUOROACETYLACETONATES AND THE TRIFLUORACETYLACETONATES OF THEMETALS COPPER, NICKEL, COBALT II AND LEAD TO ITS SUBLIMATIONTEMPERATURE, PASSING A REDUCING AGENT IN VAPOR FORM OVER THE METALCHELATE AS A CARRIER GAS, AND DECOMPOSING THE METAL CHELATE IN ITS VAPORSTATE AND DEPOSITING AT LEAST A PART OF THE METAL CONTENT OF THE CHELATEON THE SURFACE OF A SUBSTRATE TARGET MAINTAINED AT THE DEPOSITIONTEMPERATURE OF THE METAL CONTENT OF THE CHELATE.